The study, named FUSION, met its primary efficacy endpoint of superiority compared to a predefined historic control sustained virologic response (SVR) rate of 25%.

The study showed that half of the patients in the 12-week arm and 73% in the 16-week arm achieved SVR (p<0.001 for both arms).

Fatigue, headache, insomnia and nausea were the most common adverse effects reported in less than 15% of patients, the company said.

"This study demonstrates that all-oral therapy with sofosbuvir provides significant efficacy among difficult-to-treat hepatitis C patients who could not be cured by prior regimens containing pegylated interferon and now have limited treatment options," said Dr. Norbert Bischofberger, Executive Vice President of Research and Development and Chief Scientific Officer at Gilead.

Results from all four pivotal Phase 3 studies of sofosbuvir - FUSION, POSITRON, FISSION and NEUTRINO - will support the initial regulatory filing for sofosbuvir as part of all-oral therapy with RBV among genotype 2 and 3 treatment-na�ve, treatment-experienced and interferon-intolerant HCV patients, and for sofosbuvir in combination with RBV and pegylated interferon among treatment-na�ve patients with genotypes 1, 4, 5 and 6, the company said in a statement.

"With positive results from all four Phase 3 trials now in hand, Gilead is on track to meet its goal of filing regulatory applications in the United States and Europe in the second quarter," Dr. Bischofberger added.

Gilead said it will present full data from the four studies at a future scientific conference.